[GRASS5] zlib and raster rows

[Glynn Clements]

Andrea Antonello wrote:

> It complains about the fact that it doesn't recognise the
> compression method. "java.util.zip.DataFormatException: unknown
> compression method"

Do you need to tell java.util.zip what the compression method is?

Note that the compressed data doesn't include any kind of signature
(unlike a .gz file, which has a gzip header preceding the compressed
data). GRASS knows when the data is zlib compressed (i.e. if the map
is floating-point and the "compressed:" field in the cellhd file has a
positive value).

BTW, there is also a flag byte at the beginning of each row (either
'0' or '1', i.e. 48 or 49), which indicates whether the compressed
data is actually compressed.

-- 
Glynn Clements <glynn.clements at virgin.net>